Spectral sentization of photosensitive compositions

ABSTRACT

As a spectral sensitizer for photosensitive compositions containing a photolyzable organic halogen compound, at least one aromatic polycyclic compound having an ionization potential below about 7.4 is used. Preferred are colored, linear fused-ring polynuclear carbocyclic compounds (acenes) which are essentially unreactive with the organic halogen in the dark under room conditions.

0 United States Patent 51 3,640,718 Smith 1 Feb. 8, 1972 I54! SPECTRAL SENTIZATION OF [561 References Cited ml Wile 5mm, Maplewwd' 3,526,506 9/1970 Workman ..96/90 [73] Assignee: Minnesota Mining and Manufacturing P i, U Ex mi r Norman G To hin r no a ne rc Company Paul Assistant Examiner-John Winkelman [22] Filed: Apr. 10, 1968 Attorney-Kinney, Alexander, Sell, Steldt & Delahunt As a spectral sensitizer for photosensitive compositions con- [52] US. Cl. ..96/89, 96/1 R, 96/48 HD, mi i a photolyzable organic halogen compound, at least one 9 /63, 9 9 0, 9 P aromatic polycyclic compound having an ionization potential [51] Int. Cl ..G03c 1/72 below about 7.4 is used. Preferred are colored, linear fused- [58] Field of Search ..96/88, 89, 90, 115 P ring polynuclear carbocyclic compounds (acenes) which are essentially unreactlve with the organic halogen in the dark under room conditions.

9 Claims, No Drawings SPECTRAL SEN'IIZATION OF PHOTOSENSITIVE COMPOSITIONS This invention relates to a new class of sensitizers for the unreactive with said organic halogen compounds in the dark under ambient conditions, i.e., they are stable for periods of at least 3 months, preferably at least 6 months, under ambient conditions in the dark. For example, they are most preferably photolysis of organic halogen compounds. In particular this infree of amine groups which react with organic halogen comvention relates tosensitizers which extend the photolysis of orpounds in the absence of light. Illustrative aromatic polycyclic ganic halogen compounds to higher wavelengths of light. sensitizers meeting the aforementioned criteria include: Organic halogen compounds are widely used in the graphic perylene; rubrene; 2-ethyl-9,IO-dimethoxyanthracene; arts field to produce commercially useful photosensitive contetraphenylpyrene; tetra'cene; pentacene; coroncne; benzo-astructions. They may be used as photoinitiators for free radical l0 'pyrene; benzo-a-naphthonapthracene; dibenzochrysene; photography (e.g., printout and bleach systems), free radical benzopentaphene; rubicene; benzoperylene; trimethylazuphotopolymerization, cationic photopolymeriz'ation and lene; decacyclene; diphenylanthracene; etc. The most photoinduced acid catalyzed reaction of many types. Various preferred sensitizers are nonpolymeric, colored compounds. photosensitive products useful in printing, duplicating, copy- Photolyzable organic halogen compounds capable of ing and other imaging'systems can be prepared withsuch orgenerating free radical halogen under the influence of light are ganic halogen compounds. :known. Preferred photolyzable organic halogen compounds Organic halogen compounds are known to photodissociate are nongaseous (i.e solid or liquid) at room temperature and to give free radical halogen, such as free radical bromine and have a polarographic half wave reduction potential above chlorine, which are good hydrogen abstractors and which will about 0.9. Illustrative are hexabromoethane, tetrabromo-oproduce acid in the presence of hydrogen donors. Their use in xylene, dibromotetrachloroethane, tribromotrichloroethane, photopolymerization processes is described in Light Sensitive pentabromoethane, dibromocyanoacetamide, tris- Systems: Chemistry and Application .of Nonsilver Halide Photojtribromomethyl-triazine, dibromodibenzoylmethane, graphic Processes, .l. Kosar, J. Wiley & Sons (New York, triiodomethane, tetrabromodifluoroethane, tribromoquinal- 1965), pages 180-181. Both the free radical halogen and the dine, hexachloro-p-xylene, etc. photoproduced acid have been used in various systems involv- Although the concentration ratio of sensitizer to organic ing the photochemical formation and destruction of dyes, see halogen compound is not critical, generally the molar ratio is the above Kosar citation, pages 361-370. between 1/20 to 2/1, respectively, for maximum speed. The use of sensitizers to broaden the spectral response of Coatings, layers, films or sheets made with solutions of these organic halogen compounds is known, and yellow azo dyes, organic halogen compounds and sensitizers, normally with a styryl and leuco dye bases, and cyanine dyes are suitable for binder, are unusually stable and can be stored for long periods this purpose. Unfortunately most of such sensitizers cause under ordinary room conditions. The resulting constructions serious stability problems under normal storage conditions absorb light well into the visible light spectrum. These senprior to the use of the photosensitive sheet or film. Many of sitizers are soluble in organic solvents such as acetone, methyl these known sensitizers contain a basic group, such as ethyl ketone, monomethyl ether of ethylene glycol, etc., and dimethylamino, which chemically reacts with the organic 5 are easily prepared and purified. Moreover, the high efficienhalogen compound, resulting in a reduction in or loss of cy of these sensitizers makes it possible to use less expensive photosensitivity, e.g., premature acid formation. Other known and nontoxic organic halogen compounds. sensitizers, such as the cyanine dyes, are salts of strong acids To illustrate the invention, solutions containing both 10 M and weak bases which, because of their acidity, will react with 'of organic halogen compound and about 10" M of sensitizer acid-sensitive components in the photosensitive system during 40 in acetone were prepared. Twenty milliliters of each solution storage. Moreover, because dyes in salt form are generally inwas exposed through a filter (Corning C.S. 3-74) which transsoluble in organic solvents, they are often difficult to formumits light of wavelength greater than 390 millimicrons so that late and coat. Many can be made only be complicated synthesonly the sensitizer was absorbing light. For the light exposure a is and are expensive to prepare and to purify. Leuco dyes medium pressure mercury vapor lamp (GEH3T7) was used to bases, besides being basic, are sensitive to oxygen and are provide 0.07 Watts/ mf in ident energy. After P ur 2 therefore difficult to purify and to store. The yellow azo com ml. of each exposed solution was added to 1 ml. of an acidpounds are restricted in their absorption of light and in many as i d at r S lution of 0.005 g. of 4-phenylazo-1- cases do not effectively sensitize organic halogen compounds. naphthylamine in 100 ml. of isopropanol. The resulting solult is therefore an object of this invention to provide a novel tions were then diluted to 10 ml. with isopropanol and the visisensitized photosensitive element having photolyzable organic [ble absorption spectra were measured. The log of the ratio of halogen compounds. the two peaks was determined as NB where A is the ab- Another object of this invention is to provide sensitized sorption at 540 my. (acid form) and B is the absorption at 437 compositions containing photolyzable organic halogen commu (base form). This value was then used to determine the pounds. amount of acid generated by comparing it to a previously Still another object of this invention is to provide novel 5 calibrated straight line plot of acid concentration vs. log A/B, photosensitive copysheets and improved processes for their which was obtained by adding known amounts of acid solution manufacture and use. (p-toluenesulfonic acid) to the dye solution and measuring the In accordance with this invention it has been found that absorption peaks. The straight line portion of the plot occurs photolyzable organic halogen compounds are sensitized to between the acid concentrations of 2X10- M, and 9X10 M, higher wavelengths of light in solution by one or more aroand the exposure time was adjusted to produce concentrations matic polycyclic compounds which have an ionization potenof acid in that range. Table 1 shows the results obtained with tial below about 7.4 these sensitizers are desirably essentially ,gr eg tative organic halogen compounds and sensitizers.

TABLE 1 Wave Exposure Acid Organic halogen Concentration, sensitizer lengths, time, concentration, compound (M) sensitizer concentration, (M) (mp) (sec.) (M) (121311: Total 5,5)(10- (3 1m. 390 10 None (1 1ml. 300 10 asuxnr mun 300 10 iunxur (32MB 390 10 437x10 11hr 390 115 3150x10- (win-, 39 30 3128x10- 'lolrul rmuo-o-xylmm 390 30 6.MX10-5 lluxucliloro-p-x ylono. 390 2.0?!)(10' 'lutraln'omo-o-xyluno. 390 10 40x10" 'lotrubromo-o-Xylene... m, 7 X 07. 2 90 -M)S TABLE I.-Cntinued I Wave Exposure Acid Organic halogen Concentration, I Sensitizer lengths, time, concentration, compound (M) Sensitizer concentration, (M) (1m) (sec) (M) Te'trabromo-o-xylene. u 'LXIO- Benzonaplithonapthacene i 2 '7.X10- 390 3O 20BX10- letrabromo-o-xylone 7. XIO- Dlbenzpyrene (1,2,4,5) 2 7. X- 390 30 3.2)(10- 7.X10- Rubrene 2 7. 0' 390 8 7.1)(10- 7. X10" Coronene. 2 7.X10- 390 20 1.6)(10- 72x10 Perylene 2 7-)(10' 390 1O 8.0X10- 1 Minutes. 2 Sat.

In general, the sensitization of photolyzable organic halogen portions of the original. Heating caused fusion of the colored compounds in liquid solutions occurs when the concentration toner powder, providing a positive copy of the original.

of organic halogen compound is greater than about 10 M. These sensitized photolyzable organic halogen compounds may be used as a liquid solution in an organic solvent, e.g., a The f ll i Solution was prepared photobleachable ink, or as a solid solution in an inert organic Example 2 bmder a photosensnwe layer m a copysheet' 32 grams ofa 5% solution of cellulose ethyl ether The enhanced sensrtlvrty of the photolyzable organic (Ethocel N400, a trademarked product of halogen compounds is not restricted to any particular use, Dow Chemical p y) i acetone 0.3 gram of tetrabromodichloroethane 0.1 gram Rose Bengal N (Color Index No. 45440) 0.02 gram perylene type of construction or imaging process. When coated onto a substrate with vinyl ethers, the photoproduced acid causes cationic polymerization of the ethylenically unsaturated monomer. When coated onto a substrate with acrylate esters, The above Solution was knifa coated onto a polyester film at the photoprodu ed free radlcals Cause free radical a knife setting of 4.0 mil. A SO-second exposure of a dried polymerization of the ethylenically unsaturated monomer. coated sample through a positive transparency to tungsten Tacky polymerized areas are made nontacky by toner po light of 15,000 foot-candles of incident light energy caused developmeml revealmg the wage The uflpolymel'lzed complete bleaching of the red colored Rose Bengal N dye to unexposed areas may be transferred to plain paper and then give a positive copy ofthe Original transparency powder developed to give a copy of the original light image.

The unpolymerized monomer may also be transferred to a E am le3 water receptive metal surface and then polymerized to produce a lithographic plate. In still another application the photoproduced acid is used to effect the bleaching of dyes, resulting in high resolution positive or nonreversal copies of The following solution was prepared.

3.0 grams of 5% solution of cellulose acetate butyrate in acetone transparemfil'aphic originals 0.0] gram hexabromoethane The sensitized systems of thls invention are also useful in 0.005 gram perylene conjunction with tetrahydropyranyl derivatives of aromatic I-(l-lelrahydmpymflylmyH- mcthoxynaphthalene hydroxy and amino compounds, the photoproduced acid causmg decomposition of these derivatives to generate the parent hydroxy or amino compounds which are capable of reducing silver or other metal complexes to form visible images. I Photosensitive fi lms incorporating organic halogen com giving 1000 foot-candles incident light energy. pounds which undergo photodecomposltlon may also be sen- 0 sitized in accordance with this invention. Illustrative The exposed Sample was then heated at about 100 while photosensitive films of this yp are Shown in U S Pat No in contact with areceptor sheet containing a coating of Parts by Weight It was knife coated onto a polyester film at a knife setting of 3.0 mil. A sample of the dried coating was exposed through a photographic negative for only 1 second to a tungsten light 3,08l,l65, their use being described in xerographlc image Silverbehena'e recording processes characterized as electrochemography. r Phthalazinone toner 5.2 In these processes an electrostatic latent image is formed by 1 f i z ft -g y v 3-;

. oyvrny utyra in er exposure of an electrochemographlcally sensitive surface or zinc Oxide Powder 5010 layer to yield a conductivity latent image adapted to produce Polyterprene resin 10.0

an electrostatic latent image by selective dissipation of an f electrostatic surface charge, either once or repetitively without the necessity for successive exposures to an optical The liberated 4-methoxy-l-naphthol caused selective .image. reduction of the silver behenate in the exposed areas to give a The following examples will illustrate the use of the sendense black-on-white negative copy of the original.

sitized photolyzable organic halogen compound systems of The following solution was prepared.

Example 1 The following solution was prepared. l0 ml. of 2% polymethylaerylate (molecular weight of about l00,000 in methylene chloride 1.0 gram of vinyloxyethylether of fl-naphthol gfr fiswgjgzzz 0.5 gram cellulose acetate butyrate 0.075 gram hexabromoethane I 50 ml. methyl ethyl ketone This solution was knife coated (3.0 mil wet thickness) onto a conductive backing, such as aluminum vapor coated In 4.0 ml. of the above solution was dissolved 0.003 gram of polyester film. A sample of the coated film was provided with 2-ethyl-9,lO-dimethoxyanthracene. This solution was kn a negative surface electric charge in the absence of light by coated onto a polyester film at a knife setting of 2.0 mil. A means of a negative corona discharge of 6,000 volts. The sample of the dried coating was given a Z-second exposure charged sample was then exposed through a transparent through asuitable transparency withatungsten light providing master to 100 foot-candles of incident tungsten light for 15 n l O incident gh n rgy- T exp d seconds and was placed in a standard electrostatic liquid sample was then placed against a Sheet of rdinary paper and developer bath. The toner powder in the developer was heated at C. for 5 seconds. The paper was treated with a d ited in th unexposed areas to give a positive copy of the resin coated colored toner powder which selectively adhered original master. This example illustrates the use of the sento the paper in those areas corr p ng t the unexposed sitized compositions of this invention in an image recording media for electrochemography.

Various other embodiments of the present invention will be apparent to those skilled in the art without departing from the scope thereof.

What is claimed is:

1. In a photosensitive composition containing a photolyzable organic halogen compound and at least one spectral sensitizer therefor, the improvement which comprises using as a spectral sensitizer a colored acene compound which has an ionization potential below about 7.4 and is essentially unreactive with said organic halogen compound in the dark under ordinary room conditions.

2. The photosensitive composition of claim 1 in which said photolyzable organic halogen compounds are nongaseous compounds at room temperature.

3. The photosensitive composition of claim 1 in which said composition contains a compound which undergoes a chemical change in the presence of either a free radical halogen or an acid.

4. The photosensitive composition of claim I in which said composition contains a free radical polymerizable monomer.

5. The photosensitive composition of claim 1 in which said composition contains an acid polymerizable monomer.

6. The photosensitive composition of claim 1 in which said composition contains a compound which is capable of changing color in the acid environment created upon light exposure of a photolyzable organic halogen compound.

7. The photosensitive composition of claim 1 in which the molar ratio of said sensitizer to said organic halogen compound is from 1/20 to 2/ l 8. The photosensitive composition of claim 1 in which said acene compound is free of amine groups which react with said organic halogen compound in the absence of light.

9. A photosensitive layer containing the photosensitive composition of claim 1. 

2. The photosensitive composition of claim 1 in which said photolyzable organic halogen compounds are nongaseous compounds at room temperature.
 3. The photosensitive composition of claim 1 in which said composition contains a compound which undergoes a chemical change in the presence of either a free radical halogen or an acid.
 4. The photosensitive composition of claim 1 in which said composition contains a free radical polymerizable monomer.
 5. The photosensitive composition of claim 1 in which said composition contains an acid polymerizable monomer.
 6. The photosensitive composition of claim 1 in which said composition contains a compound which is capable of changing color in the acid environment created upon light exposure of a photolyzable organic halogen compound.
 7. The photosensitive composition of claim 1 in which the molar ratio of said sensitizer to said organic halogen compound is from 1/20 to 2/1.
 8. The photosensitive composition of claim 1 in which said acene compound is free of amine groups which react with said organic halogen compound in the absence of light.
 9. A photosensitive layer containing the photosensitive composition of claim
 1. 